Electron Backscatter Diffraction Mapping Research Articles

Micro-texture regions in rolled Ti-6Al-4V under polarized light

Identifying micro-texture regions (MTR) in deformed Ti-6Al-4V requires extensive time in electron back-scattered diffraction (EBSD) imaging with a field of view that is limited to only a few millimeters. This study uses a novel method of high throughput identification of MTR using polarized light microscopy (PLM) and validation by correlation with orientation image mapping from EBSD. Reflection of polarized light under crossed polars leads to a difference in contrast depending on the orientation of the c-axis of the α-phase. MTR that are spread over a large area are visible in PLM as bands of contrast and the field of view is large compared to EBSD maps. It is shown that the shape and size of MTR may be captured accurately in PLM, and a one-to-one correspondence is demonstrated with such regions identified by EBSD with an excellent match between the area fraction of MTR calculated using both methods.

Deep Learning for automated phase segmentation in EBSD maps. A case study in Dual Phase steel microstructures

Electron Backscattering Diffraction (EBSD) provides important information to discriminate phase transformation products in steels. This task is conventionally performed by an expert, who carries a high degree of subjectivity and requires time and effort. In this paper, we question if Convolutional Neural Networks (CNNs) are able to extract meaningful features from EBSD-based data in order to automatically classify the present phases within a steel microstructure. The selected case of study is ferrite-martensite discrimination and U-Net has been selected as the network architecture to work with. Pixel-wise accuracies around ~95% have been obtained when inputting raw orientation data, while ~98% has been reached with orientation-derived parameters such as Kernel Average Misorientation (KAM) or pattern quality. Compared to other available approaches in the literature for phase discrimination, the models presented here provided higher accuracies in shorter times. These promising results open a possibility to work on more complex steel microstructures. • Deep Learning Convolutional Neural Networks were successfully applied to EBSD maps. • Beyond 98% accuracy to discriminate Ferrite from Martensite in a Dual Phase Steel • Misidentifications occurred in Widmanstätten ferrite and autotempered martensite. • Relatively few labeled EBSD maps are required for training.

Effective structural unit analysis in hexagonal close-packed alloys - reconstruction of parent β microstructures and crystal orientation post-processing analysis.

Materials with an allotropic phase transformation can form microstructures where grains have orientation relationships determined by the transformation history. These microstructures influence the final material properties. In zirconium alloys, there is a solid-state body-centred cubic (b.c.c.) to hexagonal close-packed (h.c.p.) phase transformation, where the crystal orientations of the h.c.p. phase can be related to the parent b.c.c. structure via the Burgers orientation relationship (BOR). In the present work, a reconstruction code, developed for steels and which uses a Markov chain clustering algorithm to analyse electron backscatter diffraction maps, is adapted and applied to the h.c.p./b.c.c. BOR. This algorithm is released as open-source code (via github, as ParentBOR). The algorithm enables new post-processing of the original and reconstructed data sets to analyse the variants of the h.c.p. α phase that are present and understand shared crystal planes and shared lattice directions within each parent β grain; it is anticipated that this will assist in understanding the transformation-related deformation properties of the final microstructure. Finally, the ParentBOR code is compared with recently released reconstruction codes implemented in MTEX to reveal differences and similarities in how the microstructure is described.

Observation of Retained γ Grains in TRIP Steels Using SEM-FIB/EBSD Method and Examination of Stability Evaluation Method

Morphologies of retained γ grains in TRIP steels are a very important factor for understanding the relationship between the microstructure and mechanical properties of TRIP steels. We have investigated a serial sectioning technique using a scanning electron microscope (SEM) equipped with an electron backscatter diffraction (EBSD) and a focused ion beam (FIB) to reconstruct 3D microstructure of TRIP steels. In this paper, FIB fabrication condition dependences of reconstructed 3D structures are presented in TRIP steels and γ-grains stabilities are discussed in terms of ion beam effects. Retained γ-grains are not recognized by EBSD map from a FIB fabricated surface using normal ion accelerating voltage of 30 kV, because γ grains are easily transformed into martensite due to ion irradiation. It was found that the transformation was suppressed by using a low acceleration voltage of 7 kV or less, and the three-dimensional morphology could be observed using low acceleration voltage serial sectioning technique. It becomes possible to evaluate morphology of each phase and we proposed evaluation method of γ stabilities by ion irradiation transformation.

Preservation of aragonite in Late Cretaceous (Campanian) turtle eggshell

Among amniotes, turtles are the only clade that lay aragonitic eggs. Because aragonite is a metastable mineral, unequivocal preservation of aragonite in fossil turtle eggs has only been reported from Pliocene deposits. Here, we report in situ preservation of aragonite in a turtle egg from the Judith River Formation (Campanian) of Montana, USA. We utilized electron backscatter diffraction (EBSD) and Raman spectroscopy to explore the carbonate mineral polymorphs in the eggshell. The EBSD maps show the presence of both aragonite and calcite with the former preserved as needle-like crystal, a feature of all turtle eggshells. The presence of aragonite is independently validated by Raman maps. This dual approach provides direct, unambiguous evidence that the record of aragonitic turtle eggshell dates back at least to the Campanian (ca. 76 Ma) and supports the hypothesis that aragonitic eggshell is a synapomorphy of all turtles. The presence of pristine aragonite also indicates minimal taphonomic alteration at the fossil locality. Consequently, diverse invertebrate or vertebrate fossils from localities with aragonitic turtle eggs may provide high quality, unaltered palaeoenvironmental information. • A Late Cretaceous turtle egg preserves aragonite. • EBSD and Raman spectroscopy provide independent approach. • It supports the view that aragonitic egg is synapomorphic to all Testudinata. • Judith River Formation and its equivalent strata may preserve more aragonitic fossils.

Friction stir butt-welding of roll cladded aluminum thin sheets: effect of microstructural and texture changes on mechanical properties

Experimental studies are carried out on the friction stir butt-welded aluminum (Al)-clad-aluminum thin sheets. Aluminum alloy 4343 (AA4343, Al–Si series) and 3003 (AA3003, Al–Mn series) act as the clad layer and the core of the Al-clad-Al material system, respectively. Optical microscopy confirms that the joining is achieved successfully without macroscopic defects, while the clad layer is mixed into the core, mostly in the advancing side (AS) of the stir zone (SZ). Outside the SZ, no delamination between the clad layer and core is observed. Material flow analysis with electron probe microanalyzer exhibits the flow of silicon (Si) particles from the clad layer to the core resulting in several Si-induced precipitations of α-Al(Fe, Mn)Si, α-AlMnSi inside the SZ. The heterogeneous distribution of those precipitates is visualized by scanning electron microscopy and their compositions are analyzed using an energy dispersive X-ray spectrometer. Electron back-scattered diffraction maps reveal dynamically recrystallized ultra-fine grain structures (3.7–3.9 μm) inside the SZ. The mechanical properties of the joint are evaluated by cross-sectional 2D microhardness mapping and uniaxial tensile tests. Inside the SZ, the grain refinement with the formation of Si precipitation increases the tensile strength and microhardness of the joint.

Genesis of visible gold in pyrite in the Zhaoxian gold deposit, Jiaodong gold province, China: Constraints from EBSD micro-structural and LA-ICP-MS elemental analyses

Pyrite (FeS2) is one of the most common hosts for gold (Au) in different types of gold deposits, including visible and invisible gold. For visible gold in pyrite, it remains unclear whether it resulted from remobilization of invisible gold in the gold-hosting pyrite or from external input. This paper reports a case study from the Zhaoxian gold deposit, which is the deep extension of the well-known Jiaojia gold deposit, in the Jiaodong gold province. The texture and composition of Au-bearing pyrite from the Zhaoxian deposit were studied with petrographic, Electron Back-Scattered Diffraction (EBSD) mapping, and Laser Ablation – Inductively Coupled Plasma – Mass Spectrometry (LA-ICP-MS) methods. Four types of pyrite (Py-1 to Py-4), corresponding to four generations of veins, i.e., the pre-ore V1, syn-ore V2 and V3, and post-ore V4, were distinguished. Py-2 is volumetrically the most abundant among the four, and is the main host of visible gold. LA-ICP-MS analyses of pyrite indicate that gold contents in most analysis points are below the detection limit, with measured Au contents ranging from 0.02 to 0.17 ppm (median 0.09 ppm) in Py-1, and 0.03 to 2.45 ppm (median 0.07 ppm) in Py-2. EBSD analyses indicate that pyrite (Py-2) display brittle deformation features including microstructures, lattice dislocation, and grain boundary displacement. Visible gold in Py-2 occurs in micro-fractures, cavities, and grain boundaries. The generally low contents of Au in pyrite, including Py-2, and the brittle deformation features, suggest that the visible gold grains did not result from remobilization of invisible gold from pyrite. Rather, the majority of gold was introduced by fluids after the formation of the gold-hosting pyrite. These fluids were derived from the same sources as those precipitating the gold-hosting pyrite, but were more evolved and enriched in Au. Circulation of these auriferous ore-forming fluids in microfractures of pyrite and interstitial space resulted in precipitation of visible gold.

Local Kikuchi band detection in electron backscatter diffraction patterns for enhanced pattern indexing.

Partially missing bands in the preset region for Hough transform might strongly affect the accuracy of indexing Kikuchi patterns and reduce the quality of electron backscatter diffraction (EBSD) maps. This paper proposes a novel local band detection method for such kind of low-quality patterns. The approach involves rotating bands to vertical direction, detecting the local line segments through calculating the largest horizontal average grey gradient with a constant interval of 400 pixels in vertical direction, and applying Hough transform as well as weighted averaging to these line clusters to unify the edges of Kikuchi band. Therefore, even if only part of a Kikuchi band is visible, the entire band can also be accurately extracted. The average interplanar angle error obtained by the proposed method is approximately 29.0% less than those obtained by Hough transform-based technique. Moreover, the comparison of mean angular deviation (MAD) is also discussed. The average MAD of this method is about 38.5% lower than that of Hough transform-based technique. Consequently, the local Kikuchi band detection method is expected to be used for post-processing and re-indexing the EBSD low-quality patterns.

Effects of Sm addition on microstructure evolutions and mechanical properties of high-strength Mg–Gd−Sm–Zr extruded alloys

Effects of various Sm additions on microstructures and mechanical properties of a hot-extruded Mg–14Gd−0.5Zr alloy were studied in this work. The results indicate that Sm addition firstly clearly improves the strength and then decrease as the Sm content increases at both room temperature and high temperatures. The highest yield strength was obtained to be ∼495 MPa and ∼512 MPa under tension and compression, respectively, at room temperature with the Sm concentration of 1 wt% while those were to be 384 MPa and 248 MPa at 250 °C and 300 °C, respectively, with the Sm content of 0.5 wt%. Electron backscatter diffraction mappings reveal that Sm addition significantly promotes dynamic recrystallization, resulted in much more fine recrystallized grains and lower texture intensity. Furthermore, transmission electron microscopy observations show that Sm addition increases dynamic precipitates particularly in non-recrystallized regions, leading to relatively less aging precipitates during artificial peak-aging. Finally, discussion based on grain boundary strengthening and dispersion strengthening suggests that Sm addition improving the yield strength of the extruded Mg–14Gd−0.5Zr alloy is mainly attributed to more grain boundaries and dynamic precipitates at room temperature and high temperatures, respectively.

Enabling High-fidelity Twin Pattern Prediction in Polycrystals — A Mesoscale Grain Boundary Plasticity Model.

In this paper we propose a parameter-free grain boundary (GB) model for the meso-scale, employing it to effectively capture one-to-one twin pattern development across polycrystals (for the first time), by means of crystal plasticity finite element methods (CPFEM). Our model does not require higher-order mechanics, involve limiting length-scales, or demand special considerations for its FEM implementation. It derives all its data from that of its adjacent grains, which are modeled using single crystal plasticity. We apply our mesoscale GB model to experimentally imaged microstructures of Magnesium and Titanium. We demonstrate a clear ability to capture the prominent role of GBs in the nucleation and patterning of twins, with high spatiotemporal fidelity (approaching one-to-one), as compared to electron back-scattered diffraction (EBSD) maps.

Microstructure Evolution, Mechanical, and Corrosion Behavior of Cryogenic Friction Stir‐Processed AA2014 Alloy

Herein, a large‐area stir zone (SZ) is fabricated in AA2014 alloy via overlapping friction stir processing (FSP). The microstructure and texture evolution of AA2014 alloy during FSP is examined using electron backscattered diffraction (EBSD). EBSD maps reveal recrystallized fine grains with high‐angle grain boundaries in SZ due to dynamic recovery (DRV) and continuous dynamic recrystallization (C‐DRX). Severe plastic straining induced by the tool leads to the formation of the A‐(110) <111> component. The texture component is further investigated with X‐ray analysis, and the results are reported. Mechanical testing reveals that ductility significantly increases after FSP, whereas the hardness and strength remain lower than that of base metal (BM) due to thermal softening. Corrosion studies show that the corrosion attack is significantly controlled after FSP due to the development of a homogeneous fine‐grained structure and uniformly distributed fine precipitates.

Influence of laser power on precipitate formation and multiple step transformation kinetics in NiTi shape memory alloy weld joints

NiTi shape memory alloys are considered to be one of the fastest-growing materials with vast potential. However, the broader applications in intricately designed components are limited due to difficulties faced during welding processes such as degradation of functional and mechanical properties, precipitate formation, and selective vaporization of elements. In this study, the effect of laser power on precipitates formation and subsequent transformation temperatures on NiTi shape memory alloy was investigated by testing 0.8 kW, 1.0 kW and 1.2 kW welded specimens. The microstructures revealed the formation of Ni4Ti3 precipitates in the fusion zone and energy dispersive X-ray spectroscopy assessment exhibited preferential Ni evaporation. Differential scanning calorimetry analysis revealed the evolution of multiple step transformations (3-step / 3-step) after laser welding. Furthermore, enthalpy change in peak transformations was evaluated and increasing order of enthalpy change was recorded for weld joints with increasing laser power. The kinetics of martensite transformation was evaluated by placing emphasis on average activation energy. High laser power welded joints showed easy martensitic transformation compared to low laser power welded joints. X-ray diffraction assessment also validated the existence of Ni4Ti3 precipitates and martensitic phase in NiTi alloy after laser welding. The electron backscattered diffraction maps of welded joints revealed the grain growth in the fusion zone and heat affected zone, and the unindexed black region emphasized the formation of distorted interphase of austenite/martensite and additional martensite phase at the fusion zone/heat affected zone interface.

Recrystallization Behavior and Texture Evolution in Low Carbon Steel during Hot Deformation in Austenite/Ferrite Region

The cover illustrates the recrystallization behavior and texture evolution of low carbon steel sheet by hot deformation at different temperatures. From left to right are inverse pole figure (IPF) colored orientation maps, metallographic structures and electron back-scattering diffraction (EBSD) maps of recrystallized, substructure, and deformed grains. The mechanisms and details can be found in the article number 2100047 by Bo Jiang and co-workers.

In-situ observation of single variant α colony formation in Ti-6Al-4V

Much of the current understanding of the β → α + β phase transformation in the commercially important titanium alloy Ti-6Al-4V (Ti64) is by inference from more β-stabilised analogues, or post-mortem studies. In-situ cooling experiments have been conducted for the first time on Ti64 samples, in an adapted SEM with a high temperature heating stage, while performing real-time secondary electron video recording and sequential electron backscatter diffraction mapping. This has enabled direct observation of the development of grain boundary (GB) α colony microstructures, when cooling at relatively low rates (0.3–0.1 °C s−1) through the β transus. It is shown that the α colonies develop discontinuously, with relatively widely spaced larger ‘primary’ α lamellae nucleating first at lower undercoolings at β GBs, which grow out rapidly into the grains until impingement. These primary laths form a ‘skeletal template’ for the subsequent colonies by determining the variant selected within their domain of influence, as the extent of transformation increases. This occurs through biasing the subsequent sympathetic autocatalytic nucleation of finer secondary α laths combined with branching and plate broadening, to ‘infill’ the remaining β matrix with laths of the same variant. Evidence has also been provided that is in agreement with previous studies of the crystallographic relationships between the nucleating GB α allotriomorph variants, colonies, and the β GBs. However, GB α allotriomorphs were not always found to be a pre-requirement for the development of single variant α colonies in Ti64 (at least when observed at a surface), with the primary α laths seen to nucleate directly off β GBs in competition with the GB α allotriomorphs in many cases.

Dislocation Creep of Olivine and Amphibole in Amphibole Peridotites from Åheim, Norway

Amphibole peridotite samples from Åheim, Norway, were analyzed to understand the deformation mechanism and microstructural evolution of olivine and amphibole through the Scandian Orogeny and subsequent exhumation process. Three Åheim amphibole peridotite samples were selected for detailed microstructural analysis. The Åheim amphibole peridotites exhibit porphyroclastic texture, abundant subgrain boundaries in olivine, and the evidence of localized shear deformation in the tremolite-rich layer. Two different types of olivine lattice preferred orientations (LPOs) were observed: B- and A-type LPOs. Electron backscatter diffraction (EBSD) mapping and transmission electron microscopy (TEM) observations revealed that most subgrain boundaries in olivine consist of dislocations with a (001)[100] slip system. The subgrain boundaries in olivine may have resulted from the deformation of olivine with moderate water content. In addition, TEM observations using a thickness-fringe method showed that the free dislocations of olivine with the (010)[100] slip system were dominant in the peridotites. Our data suggest that the subgrain boundaries and free dislocations in olivine represent a product of later-stage deformation associated with the exhumation process. EBSD mapping of the tremolite-rich layer revealed intracrystalline plasticity in amphibole, which can be interpreted as the activation of the (100)[001] slip system.

Severe plastic deformation as a processing tool for strengthening of additive manufactured alloys

For the first time, the novel combination of multi-pass equal channel angular extrusion/pressing (ECAE/P) and selective laser melting (SLM) was investigated. Herein, four passes of ECAP via route B c at 150 °C were applied as a severe plastic deformation (SPD) technique on the SLM as-built AlSi12 to promote superior mechanical properties. The microstructure and mechanical behavior of AlSi12 fabricated by SLM were studied before and after ECAP, applying several mechanical and microstructural characterization techniques. Results of the tensile experiments revealed that the yield point, the ultimate strength, and the ductility of the as-built sample were improved by 56%, 11%, and 55% after 4 passes of ECAP, respectively. This enhancement is attributed to the effective grain refinement and the persisting silicon phase network after SPD as evidenced by electron backscatter diffraction and elemental mapping results. Moreover, micro-computed tomography analysis disclosed that ECAP considerably reduces the remnant porosity of the post-treated SLM AlSi12 samples eventually further affecting the strength of the ultra-fine grained AlSi12 in a positive way. Findings presented herein indicate that it is viable to utilize ECAP as a post-AM processing tool for mechanical property improvement of laser powder bed fused microstructures with the virtue of enhanced densification. Even if geometrical restrictions exist in ECAP, results obtained herein are transferrable to other SPD techniques with suitable processing windows, which would pave the way to advanced properties of adequately post-treated conditions.

Investigation of the strengthening mechanism in 316L stainless steel produced with laser powder bed fusion

Of the many benefits of the additive manufacturing process, laser powder bed fusion (L-PBF) has specifically been shown to produce hierarchical microstructures that circumvent the common strength-ductility trade-off. Typically, high strength materials have limited ductility, and vice versa. The L-PBF microstructure, consisting of fine cells, is formed during the rapid solidification of the laser powder bed fusion process. The cell boundaries are often characterized by the segregation of alloying elements and a dislocation network. While there are a number of works describing the strengthening mechanisms in L-PBF-produced 316L, there are still some gaps in understanding the effect of stress-relief and annealing at various annealing temperatures (400, 800 and 1200 °C) on the plastic strain accumulation during deformation. In this study, the authors evaluated strain partitioning using electron backscatter diffraction and kernel average misorientation maps. The results show strain partitioning to be dependent on both the annealing temperature and the pre-straining of samples. Further, the results indicated that the dislocation structure was stable until 400 °C, whereas at 800 °C strain was no longer detected at the cell boundaries. Similarly, after the heat treatment at 800 °C, elemental segregation at the cell walls was no longer detectable. Upon straining, the boundaries of as-built and annealed samples at 400 and 800 °C registered accumulation of additional strain as compared to the unstrained states. The results demonstrate that even a weak array of dislocations along the cell walls can successfully pin dislocations, albeit at a reduced capability relative to the co-existent dislocation and segregate structures found in microstructures of the as-built and annealed samples at 400 °C.

Crystal plasticity modeling for mechanical property prediction of AA2195-T6 friction stir welded joints

The gradient material exposure to frictional heat and plastic flow during friction stir welding leads to local variations in microstructure and mechanical properties among different joint zones. This study aims to predict strengthening contributions of local microstructural evolutions including precipitate distribution, crystal morphologies, grain size, and dislocation density for friction stir welded joints of AA2195-T6. These effects are included by a unified microstructure-sensitive physics-based constitutive modeling approach into joint local variations in yield strength, plastic hardening, and ultimate tensile strength. Local precipitate phase distributions are observed by the transmission electron microscopy method. X-ray diffraction process is conducted to measure joint local variations in dislocation density. Electron backscattered diffraction mapping is utilized to observe joint local crystal morphologies. Evolutions in the crystal slip strength due to each of mentioned microstructure attributes are inserted into a crystal plasticity finite element frame work. Modeling parameters are calibrated for AA2195-O and T6 conditions, and simulated outputs are validated by comparing with experimentally observed joint local tensile properties using the digital image correlation method. Subsequently, obtained local tensile properties in the grain scale are inserted into a macroscale global model containing all friction stir welded joint areas. An acceptable match is observed between simulated and experimentally obtained data on local and global friction stir welded joint tensile stress-strain curves and tensile failure location.

High-speed machining tool-steel chips as an outstanding raw material for indirect additive manufacturing?

Sustainable recycling approaches are emerging topics for environmental safety of manufacturing technologies. Chips generated in high–speed machining (HSM) of as-quenched steels have a potential re-use for more sustainable and cost-efficient manufacturing routes, such as powder production from chip milling for additive manufacturing (AM). The objective of this study was to characterise tool-steel chips generated by HSM of an AISI-SAE H13 as-quenched workpiece and evaluate their potential use for powder production, as an alternative process to atomisation. Microhardness tests reveal that this type of waste has a suitable hardness for milling, which could be attributed to its microstructure. Chips were also analysed by X-ray diffraction, scanning and transmission electron microscopies, and transmission electron backscattering diffraction (t-EBSD) mapping. The microstructure of the areas adjacent to the adiabatic shear band (ASB), where intense material flow takes place, consists of thin martensite laths with high dislocation density and low angle grain boundaries (LAGB) or sub-grain regions. ASB consists of ultrafine and nanocrystalline grains. The results provide new insight on the grain-refining mechanism assisted by progressive martensite lath subdivision into small and near-equiaxed grains, as a direct result of intense strain accumulation and recrystallisation, endorsing HSM tool-steel chips as superior (nanocrystalline) and low-cost raw material for powder production.

Microstructural evolution of P92 steel in IN740H/P92 dissimilar weld joints during creep deformation

In this study, we report the microstructural development of heat-affected zone in P92 heat-resistant steel during creep deformation in cross-weld specimens with dissimilar weld joints between IN740H/P92 materials. Different specimens were prepared via the interruption of creep testing at 50, 70, and 90% of the measured creep-rupture life and were carefully examined and compared. To explain the deformation behavior, finite element analysis was performed in conjunction with softening behavior measured by electron back-scattered diffraction and hardness mapping. The FGHAZ II region defined in this study could be related to the generally known inter-critical heat-affected zone, which showed major changes in microstructure during creep deformation due to the accelerated softening by dynamic recrystallization as well as to the development of a triaxial stress state. As a result, cavity formation and growth was observed only in the FGHAZ II region, which ultimately led to fracture.